Hyponatremia in Runners: Causes and Prevention
Understand hyponatremia in runners, why overdrinking can be dangerous, warning signs, sodium balance, and safer race hydration habits before long races.
July 1, 2026 · 2 min read
Hyponatremia happens when blood sodium becomes dangerously low, often because a runner drinks more fluid than the body can handle. It is not just dehydration's opposite; it can be serious and confusing. Prevention starts with avoiding forced overdrinking, respecting thirst, and practicing a realistic hydration plan before long races. That habit keeps your hydration safer overall.
Why runners get hyponatremia
During long events, sweat removes water and sodium, while stress hormones can reduce how quickly the body clears fluid. Drinking large amounts of plain water can dilute sodium further. Risk rises when runners move slowly for many hours, stop at every aid station, take anti-inflammatory drugs, or follow advice to drink as much as possible.
Know the warning signs
- Headache, nausea, bloating, or vomiting during or after a long race.
- Swollen hands, tight rings, or unexpected weight gain during an event.
- Confusion, severe fatigue, dizziness, or unusual behavior.
- Worsening symptoms despite continued drinking.
- Seizure or loss of consciousness, which requires emergency care.
Prevent overdrinking
- Do not drink at every aid station automatically if you are not thirsty.
- Estimate sweat rate in training by weighing before and after long runs.
- Use electrolytes during long hot races, especially if you are a salty sweater.
- Avoid gaining weight during a race; that suggests fluid intake is too high.
The weight-gain warning
If you finish a long run or race heavier than you started, you likely drank more fluid than you lost. That pattern can raise hyponatremia risk.
Respond carefully if symptoms appear
Hyponatremia symptoms can overlap with dehydration, which is why severe or unusual signs need medical assessment. Do not keep forcing water if you feel bloated, nauseated, confused, or swollen. At races, seek medical staff. For severe neurological symptoms, emergency treatment is required.
Safe hydration is not about drinking the most; it is about matching fluid and sodium to the day. Practice in training, trust thirst as useful feedback, and be especially careful in marathons, ultras, and hot races where well-intentioned overdrinking becomes a real risk.
Frequently asked questions
What causes hyponatremia in runners?
It is usually caused by drinking too much fluid relative to losses, which dilutes blood sodium. Long race duration and plain-water overdrinking increase risk.
What are symptoms of hyponatremia during a race?
Symptoms can include headache, nausea, bloating, swollen hands, confusion, vomiting, dizziness, and in severe cases seizures or loss of consciousness.
How can runners prevent hyponatremia?
Avoid forced overdrinking, drink to thirst and a tested plan, include sodium when appropriate, and check that you are not gaining weight during long efforts.
Put it into practice
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